High-vacuum diffusion pump



March 28, 1961 HANS-GEORG NLLER ET AL HIGH-VACUUM DIFFUSION PUMP Filed Deo. 1, 1958 Inc/enfans:

HIGH-VACUUM DIFFUSION PUMP Hans-Georg Nller and Werner Bchler, Koln, Germany, assignors to E. Leybolds Nachfolger, Koln-Bayental, Germany Filed Dec. 1, 1958, Ser. No. 777,378

Claims priority, application Germany Dec. 9, 1957 4 Claims. (Cl. 230-101) The present invention relates to high-vacuum diffusion pumps.

In the operation of mercury-vapor pumps a loss of mercury occurs when air is permitted to pass into the high-vacuum side of the pump. A portion of the mercury passes through the pre-vacuum junction in the form of gas or of minute droplets and condenses inside of the adjoining connection line to the pre-vacuum pump or inside of the latter itself. Such loss of mercury is extremely undesirable, particularly because this loss can be quite considerable if air is frequently let into the highvacuum side of the pump. This loss of mercury may occur to such an extent that, finally, the pump contains insuicient mercury and no longer operates.

It is known in the art to arrange baffles on which some of the mercury vapor is condensed, which ba-les are located within the pre-vacuum junction line in the path of the emerging stream of gas and vapor. The condensed mercury is then returned to the boiler of. the pump, so that the loss of mercury is reduced. If, however, such baffles and condensing surfaces in the prevacuum line are designed so as to actually reduce the mercury loss to a minimum, they also have a noticeable throttling effect on the stream of gases being pumped oif, which throttling effect should be avoided as far as possible.

In the case of oil-diffusion pumps lled with a nonhomogeneous organic working uid, it is also known to pass the tubular pre-vacuum junction line around the pump body, in good thermal contact with the latter, in the form ofa circular sector so that a pre-vacuum region is formed which is kept at constant temperature along the direction of flow. This precaution is intended to prevent the condensation and separation of the more volatile components present in the vapor of the working Huid, which interfere with the operation of the pump,.so that said components may be pumped off to the outside air by the pre-vacuum pump joined to the pre-vacuum connection.

This invention is based on a dierent approach. Here, the vapors of the pumping fluid, particularly mercury, are to be separated from the gas to be pumped out as completely as possible in a cooled pre-vacuum separation chamber, and these vapors are then to flow back in the form of a condensate into the pumping fluid reservoir. The presently known designs of oil-diffusion pumps do not permit such flowing back.

It is an object of the present invention to provide a device for reducing the loss of pumping lluid at the side of the pre-vacuum junction of a fluid pump, especially a mercniy-vapor pump, in which the outlet of the prevacuum pump stage opens into a pre-vacuum separation chamber surrounding the cooled tubular pump cover in the form of a hollow cylinder.

According to one aspect of the invention, this outlet of the pre-vacuum stage is joined to a curved outlet pipe, the mouth of which extends into the cooled pre-vacuum separation chamber. This curved pipe is so designed with respect to its outlet cross section and its position within the pre-vacuum chamber, that within the latter a Patented Mar. 28, 1961 circular owcf gas and vapor is produced. By means of this circular ow of the gas-vapor mixture, the heavier molecules therein or the minute droplets of the fluid are carried to the outer Wall of the pre-vacuum chamber, due to the centrifugal force. These heavier molecules and droplets coagulate at the cooled surface of the cham` ber. Within the circular pre-vacuum'chamber, the flow of gas and vapor is less than in the outlet tube due to the much larger cross section of the former, with the result that heavy molecules ,or minute droplets are no longer carried along into the pre-vacuum line by the stream of gas. n

The outlet pipe may have the most Varied shapes and cross sections. It is essential that the gases and vapors emerging from'the mouth ofthe outlet tube into the prevacuum separation chamber are set into circular motion within this chamber. Under certain conditions, it can be of advantage to have the outlet pipe spiral outwardly inside of the pre-Vacuum chamber, so that at rst a spiralshaped flow of gas and vapor is produced which, after impinging upon the inner surface of the pre-vacuum chamber, changes into a circular flow.

By means of such a device, the pre-vacuum separation chamber can bev connected to the pre-vacuum junction of the pump with a pipeline located at least partially within the cooling jacket of the pump. Here, the pipeline can enter substantially at right angles to the plane of the circular flow of gas and vapor in the chamber.

This invention results lin a very considerable reduction in the loss of pumping iluid at the pre-vacuum junction, whereby only a small throttling effect is exerted on the gas to be pumped. The pump permits access of air into the high-vacuum side frequently, without noticeable loss of pumping fluid.

It can also be of advantage to design the curved outlet pipe in such a manner that the angular vector with respect to the pump axis between the outlet in the tubular pump cover of the pump and the mouth .of the outlet pipe in the pre-vacuum separation chamber is at least and, preferably, more than 120. The outlet pipe located within the pre-vacuum separation chamber has an essentially circular shape and is preferably positioned closer to the outer wall then to the inner wall of this pre- Vacuum separation chamber. Such a location results in an especially good separation of pumping uid and gas. It is of advantage to position the outlet pipe in the bottom region of the pre-vacuum separation chamber, and to provide the inlet of the pre-vacuum connecting pipeline in the regionof the top of the pre-vacuum separation chamber.

The outlet pipe may have a varying instead of a constant cross section; for example, it may be funnel-shaped.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications Within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawing:

Figure 1 shows a cross section through a mercuryvapor pump with -a device in accordance with the invention.

Figure 2 illustrates a cross section along the line A-B of a mercury-vapor pump according to Figure 1.

In the embodiment according to Figure 1, a threestage mercury-vapor pump is shown, in which an inner part 1 comprising diffusion and vapor-stream stages is provided within a condensing jacket 2 which is sur? rounded by a cooling jacket 3. This cooling jacket is. connected to a cooling system (not shown) by an inlet pipe 4 and an outlet pipe 5 and has a stream of liquid coolant continually passing therethrough. In the region ofthe bottom of the cooling jacket 3, an annular pre-vacu um separating chamber or box 6 is shown, into which an outlet pipe 7 opens. This pre-vacuum chamber o is connected to a pipeline 8 leading to a pre-vacuum connector flange 9 of a working-fluid pump (not shown).

rThe exact position of the outlet pipe i in the prevacu-urn chamber 6 is illustrated vin the cross-sectional view of Figure 2. The outlet pipe 7 extends in circular form from an outlet 10 near the lower end of the condenser jacket 2 of the pump, into the pre-vacuum chamber 6. The orifice 71 of the outlet pipe 7 is angularly offset by an angle of 120 against the outlet 10 in the condenser jacket 2.

The greater part of the pipeline 8 leading to theprevacuum connection flange 9 is positioned within the cooling jacket 3, so that vapors which may enter into this pipeline S are condensed `and flow back into the pre-vacuum chamber 6 in the form of a ycondensate of the working fluid. The reduction in the loss of mercury which is attainable with the device according to the invention is very considerable. Experiments have shown that the efficiency, with respect to loss of mercury, of a mercury-vapor pump constructed as outlined above exceeds the efliciency of prior-art pumps having baffles and condensing surfaces in the pre-vacuum line, by a factor` of about 10.

We claim:

1. A mercury ejector diusion pump utilizing a pumping uid and comprising, in combination: pumping means having diusion and vapor-stream stages and a condensing jacket surrounding said stages, said condensing jacket having an inlet at the upper end and an outlet near the lower end; an annular pre-vacuum separatingv box surrounding said condensing jacket including said outlet thereof; a cooling jacket surrounding said condensing jacket and said pre-vacuum separating box; a curved outlet pipe having twoorifices, said outlet pipe being connected at one orifice thereof to said outlet of said condensing jacket and opening at the otherV orifice within said separating box for producing a circular flow of the pumping uid while the same passes from said outlet through said outlet pipe and into said separating box; and a pre-vacuum connecting pipeline arranged within said cooling jacket and communicating with the interior of said-,pre-vacuum separatingtbox.

2. A pump according to claim l wherein said curved outlet pipe has such a length that its orices are angularly offset relative to each other by an angle greater than 90.

3. A pump according to claim 2 wherein said angle is 120.

4. A pump according to claim 1 wherein said outlet pipe is positioned at the bottom of said pre-vacuum separating box and wherein said connecting pipeline termi nates at the .top of said pre-vacuum separating box.

References Cited in the tile of this patent UNITED STATES PATENTS 1,712,595 Van Der Pool May 14, 1929 2,714,484 Carr Aug. 2, 1955 2,931,561 Hiesinger Apr. 5, 1960 FOREIGN PATENTS 117,803 Switzerland Dec. 1, 1926 301,905 Great Britain Ian. 23, 1930 

